1. Field of the Invention
Our invention relates to the field of audio test equipment, and more particularly to pneumatic audio frequency generators.
2. Description of the Prior Art
Laboratory audio frequency generators are normally electronic devices. Their components include speakers, coils, switches, etc., all of which naturally produce undesirable electromagnetic interference. The quality of any test is lowered, and the accuracy of test results is reduced, by the extent to which the frequency generator interferes with the operation of the equipment which is being tested. As an ideal, a frequency generator would produce no electromagnetic interference whatever.
Many types of audio equipment are intended primarily to receive and transmit the human voice. When these devices are to be tested, the test frequencies normally range from 300 hz to 3000 hz. Electronic frequency generators operating in this frequency range produce the undesirable effects noted above. Obviously, all electromagnetic interference could be eliminated merely by having an individual speak directly into the device to be tested. This method unfortunately introduces other equally undesirable problems, however. For example, the test volume and frequency are not precisely controllable. In most cases, any given individual would be unable to produce all necessary frequencies, and certainly not with any degree of precision.
There is a need for an audio frequency generator which is entirely free of electromagnetic interference. Other desirable features would include convenient adjustability for volume, frequency, range, and frequency sweep characteristics.